Ulbricht was arrested October 1 at the San Francisco public library. Photograph: Vicki Behringer/AP

A San Francisco man has been ordered held without bail in New York after a prosecutor accused him of running a massive online drug empire and paying $730,000 to try to kill six people.

Assistant US attorney Serrin Turner made the comments to a magistrate judge during a bail hearing Thursday for Ross William Ulbricht. Turner says Ulbricht operated the Silk Road website where every type of illegal drug was sold.

Ulbricht was arrested October 1 at the San Francisco public library. He is awaiting trial on charges that carry a mandatory minimum of 10 years in prison and a maximum of life.

His mother, Lyn Ulbricht, said outside court that her son "is not a murderer."

The prosecutor says he does not believe any of the killings have occurred.